Current-limit relay



R. E. DE CAMP.

CURRENT LIMIT RELAY. APPLICATION FILED JUNEZI. 191a.

PatentedSept. 27,1921.

3 SHEETS-SHEET 1.

INVENTOR ATTbRNEY R. E. DE CAMP.

CURRENT LIMIT RELAY. APPLICATION FILED mm; 21. 1918.

Patented Sept. 27, 1921.

' 3 SHEiTS-SHEET 2.

INVENTOR wnNzssss; 60/. 1m

Fa 5056mm ATIIQRNEY R. E. DE CAMP.

CURRENT LIMIT RELAY.

APIPLICATION FILED )UNE 21, 1918.

Patentedsept 27, 1921.

3 SHEETS- -SHEET 3.

INVENTOR 1%: y f. 05 6'31 mp ATi'ORNi-IY UNITED STATES PATENT OFFICE.

RAY E. DE CAMP, OF WILKINSBURG, PENNSYLVANIA, ASSIGNOR TO WESTINGHOUSE ELECTRIC 8; MANUFACTURING COMPANY, A CORPORATION .OF PENNSYLVANIA.

CURRENT-LIMIT RELAY.

Application filed June 21,

To all whom it may concern:

Be it known that I, RAY E. De CAMP, a citizen of the United States, and a resident of lVilkinsburg, in the county of Allegheny and State of Pennsylvania, have invented a new and useful Improvement in Current- Limit Relays, of which the following is a specification.

My invention relates to electromagnets and electromagnetically actuated switches for the control of electric circuits. Ina more limited aspect, my invention relates to switches that are particularly adapted for unit-switch-control systems.

Control systems of the unit-switch type, largely used for governing electric motors, comprise a plurality of independently operated individual switches designed and connected to act successively to produce a gradual acceleration of the motors with which they are associated. Inthese systems, devices are ordinarily employed for delaying the action of the successive switches in order to avoid injuring the motors by excessive currents. One form of these devices comprises a plurality of auxiliary switches or relays mechanically interlocked with the main switches, so that it is impossible to close any main switch before the closing of the preceding switch of the series. It is found 1n practice, nevertheless, that, though each switch closes before the corresponding relay can cause the closing of the next succeeding switch, there is usually not a sufficient time interval between the closing of two successive switches to prevent excessive current peaks. i

To lengthen the time intervahthe relays are, in some systems, provided with holding coils energized by the motor current, which coils have a tendency to keep'the relays open until the armature currentreaches a predetermined safe value. Such systems, however, have not proved entirely satisfactory. For one reason, the necessary mechanical interlock between the switch and the relay complicates the apparatus, adds to the expense, and increases the liability of failure of the'apparatus to functionproperly. The current, furthermore, does not always rise rapidly enough to so energize the'holding coils as to prevent the relays from closing prematurely, and it thus happens that, as there is nothing to limit the operation of these relays except the inherent time element Specification of Letters Patent. Patented Sept. 27, 1921.

1918. Serial No. 241,259.

of the relays themselves, sections of the re- SlStQI a current-limit accelerating relay which i will avoid these defects. Myrelay is biased toward closed position, but is maintained in open position until the motor current falls to the proper value. In one form of my invention, the peak value of the current is employed to compress a spring which, thereupon, 'allows the relay to close as soon as the current reaches a previously selected safe value. The motor circuits may be so arranged, however, that the magnetism of the actuating coil ofv the relay shall perform the function of the spring, this magnetism serving both to open the relay, in opposition to the biasing force, and to maintain the relay in open positionnntil it is permitted to close by the conditions of the motor circuit. In either case, the current itself is made to perform the work of releasing the relay at the proper time. i

Anobje'ct of my invention is to provide a novel device for operating the relays of a motor-accelerating system.

Another object of my invention is to rovide a single controlling means for tliese relays. l I V Other objects of my inventionwill be inade clear from the following description, when taken in connection with the accompanying drawings, in which Figure 1 is a side elevation, and Fig. 2 an end elevation of one form of myinvention; Fig. 3 is a detail of a modification; Figs. .4, 5and 6 are, respectively, a side and an end elevation and a plan view ,of another modification; Fig. 7 is a detail of still another modification, F 8 is a diagrammatic view ofcircuits and apparatus illustrating the operation of the modification shown in Figs. 4, Sand 6'; Figs. 9, lOand 11 are views, corresponding to Figs. 4, 5and 6, of a switch adapted for alternating-current work; Fig.110

12 is a cross sectional view of a detail, taken along the line 1212 of Fig. 9; Fig. 13 is a view of the laminated bracket of Fig. 9, looking in the direction of the arrow 18, and Fig. 14 is a similar View, looking in the direction of the arrow 14, Fig. 9.

Referring to Figs. 1 and 2, an insulating base or panel 1 carries brackets 2 and 3, supporting a coil 4 which, when energized by current flowing through it, creates a mag netic field for attracting two armatures 5 and 6. A compression spring 7 is mounted upon a non-magnetizable rod 8, and the force exerted by it may be adjusted by means of non-magnetizable nut 8. The rod 8 is slidably mounted in projections 9 and 10, which are rigidly connected to. or are integral parts of, the bracket 3. The projections 9 and 10 serve also as pole pieces for the armatures 5 and 6. The upper end of the rod 8 projects through an opening in the armature 6 and is provided with an enlargement or stop 11 for normally engaging this armature. The spring 7. thus normally maintains the armature 6 adjacent to the pole piece 10, but may be separated therefrom by a non-magnetizable bushing or spacer 12 to prevent freezing.

One end of the armature 5 is provided with ears 13, which are pivotally mounted upon a shaft 14, secured to the bracket 2. A. spring 14 may be mounted upon the shaft 14, as indicated in Figs. 4 and 9, for normally maintaining the armature 5 in contact with the lower end of the rod 8, and an adjustable stop 15 may be provided for limiting its downward movement.

The upper end of the bracket 2 carries a non-magnetizable, U-shaped member 16, in the arm of which is mounted a shaft 17 to serve as a pivotal support for the armature 6. The ends of a spring 18, which is coiled about the rod 17, respectively engage the member 16 and the armature 6 to bias the free end of the armature 6 toward the panel 1. As shown in Fig. 1, an iron screw or other magnetizable member 19 is supported between the arms of the U-shaped member 16 and is longitudinally adjustable to vary the size of the gap 20 between its inner end and the adjacent end 21 of the armature 6. The free end of the armature 6 carries a cross-piece 22 that is preferably loosely mounted at 23 to permit uniform contact between its end 24 and 25 and the stationary contact members 26 and 27 of the relay, the latter members being rigidly secured to the panel 1. The contact members may be employed to close the circuit of the actuating coil of a switch (not illustrated) or may be used for other purposes.

If desired, the gap 20 between the armature 6 and the bracket 2 may be kept constant, in which case a non-magnetizable longitudinally adjustable member, such as a screw 28 (Fig. 3) may be substituted for the magnetizable member 19, the member 28 being connected to a projection 29 on the armature 6 by a spring 30. By varying the tension of the spring 30, as by means of a nut 31, the same effect may be attained as by varying the gap 20 of Fig. 1.

v If desired, however, the tension of the spring and the size of the gap may both be varied.

The operation is as follows: Upon current flowing through the coil 4, a magnetic field is created which causes the armature 5 to be drawn toward the pole piece 9. The rod 8 is thereupon forced upwardly toward the panel 1 to compress the spring 7 and force the stop 11 away from the armature 6. It the current is above a previously selected safe value, the magnetic field will overcome the force of the spring 18 or the spring 30, as the case may be, and the armature 6 will remain in engagement with the pole piece 10. The ratio of the force exerted by the magnetic field and that exerted by the spring 18 or the spring 30 may be varied, as above described, by adjusting the member 19 or the member 28, as the case may be. When the current falls to the safe value, the spring 18 or the spring 30 will move the armature 6 upwardly with a relatively quick snap movement and thus cause the members 24 and 25 to respectively engage the terminals 26 and 27. In the event that the magnetic field becomes too weak to hold the armature 5 in its elevated position, the spring 7, being released, will separate the switch members 24 and 26 and 25 and 27 with a relatively quick snap movement. By utilizing a plurality of relays of this character, the acceleration of the motor may be advantageously accomplished, and the action of each relay, if properly designed, will be delayed until the current traversing the motor circuit has decreased to a safe value.

The function of the spring 7 is obviously to insure that the armature 6 shall occupy its open position at the moment when current is first supplied to the motor and thereafter until the magnetic field created by the current flowing through the coil 4 builds up suiiiciently to move the armature 5 against the force exerted by the spring. The armature is then maintained in its open position by the force of the magnetic field, although released from the action of the spring. The spring 7 may, of course, be replaced by some other initial holding force. For example, the motor circuits may be so designed as to cause the energization of the coil 4 when the motor controller occupies its off position, and at a sufliciently high value to efi'ect movement of the armature 6 in opposition to the force of the spring 18. The spring 7, the rod 8 and the armature 5 may then be omitted, as their functions will be performed by the magnetism of the coil scribed made to do the work of a large number of relays. I have illustrated such a switch in Figs. 4, 5 and 6.

The armature 6 is replaced by any desired number of armatures 6a, 6b and 60, arranged in any desired way near the coil 4, but all controlled by the single armature 5 through the operation of the spring 7, as heretofore described in connection with Fig. 1. The stop 11 consists, inthis case, of a bar engaging all the armatures 6a, 6b and to normally maintain the movable switch members in open-circuit positions. Each armature 6a, 6b and 60 supports a non-magnetizable member 29 to each of which is attached one end of a spring 30, the other end of which is connected to a longitudinally adjustable member 28, as dein connection with Fig. 3. The springs 30 may be adjusted to different tension values, so that the armatures 6a, 6b and 60, when released by the armature 5, will be successively operated in accordance with successively lower values of the magnetic flux. The members 29 project through their respective armatures. to normally engage the pole piece lOand thus: serve as stop members 32 for. the armatures. Being made of non-magnetizable material, the stop members serve also the purpose of the bushing 12 of Fig. 1. Adjustable magnetizable members 33 regulate the air gaps 34 between the pole piece 10 and the respective armatures. An additional rod 35 may be fixed to the bar 11 so as to slide through an opening in the pole piece 10 and thereby prevent the bar from turning. V

The current in the coil 4 creates a magnetic field which attracts the armature 5, causing it to move from the. normal position illustrated in Fig. 4 into engagement with the pole piece 9. The'force of the spring 7 is. thereupon overcome, and the bar 11 is moved out of engagement with the armature 6a 6b and 6c, the stop members 32 of which are nevertheless maintained in engagement with the pole piece 10 until the flux of the magnetic field becomes successively 'su'tli Ciently low to permit the springs 30 to successively actuate the movable switch members. of: the relays with a relatively quick snap movement, to their closed-circuit positions as described in a co-pending application by H. D. James, control system, Serial No. 260950, filed Nov.4, 1918, and assigned to the Westinghouse Electric &. Manufacturing Co. The closing of corresponding relays causes the closing of successive switches. In the above-namedapplication, a second coil 36, mentioned below, is illustrated for a purpose therein described.

The armature 5, in addition to performing the function described, may, like the other armatures, control the movements of switch members. I have illustrated one method of eii'ecting this control in connection with the structure illustrated in Figs. 4, 5 and 6, but it will be obvious that the relays of the other figures illustrated in this application may be correspondingly changed, if desired. The armature 5 is provided with an extension 37, preferably of insulating material, which carries a switch member 38 for cooperating with stationary switch members 39, mounted upon the insulating panel 1. The switch member 38 may, of course, be mounted on the body portion of the armature 5.

In Fig. 8, I have diagrammatically shown a system in which the device of Figs. 4, 5 and 6 may be employed. A motor, comprising an armature 40 and a shunt field-magnet winding 41, is connected between line conductors 42 and 43, with an accelerating resistor 44 in series with the armature 40. A portion 4a of the coil 4 is connected across the terminals of the resistor 44. The movable members of switches 45, 46 and 47 are adapted to be actuated by coils 48, 49 and 50 to cause the short-circuiting of successive portions of the resistor 44. The coil 48 is connected in a circuit leading from the line conductor 42 through the switch 51, the

armature 6a, and the stationary contact terminal 26 that is adapted to be engaged by the movable contact member 24 or" the armature 6a, to the line conductor 43. The coils 49 and 50 are similarly connected to the armatures 6b and 60, and the other portion 36 of the coil 4 is connected in the circuit of the coil 50. The movable member of line switch Upon closing the start switch, a circuit isestablished from the line conductor 42,

7 through the stop and start switches, contact members 39 and 38, and coil 52 to the line conductor 43. The switches 51 and 5 3 are closed because of the energization ot' the coil 52. The start button may now b'e released, the coil 52 remaining energized by the closed circuit extending from the line conductor 42, through the stop ush-button switch, the switch 53, and the coil to the line conductor 48. The closing of the switch 51 closes a circuit through the motor extending from the line conductor 42, through the switch 51, the armature 40 and the resistor 44, and the field-magnet winding 41, in multiple, to the line conductor 48. A circuit is also established through the coil 46; in parallel relation to the resistor 44.

The energizing of the portion 4a of the coil 4 creates a magnetic field which attracts the armature 5 to the pole piece 9, which, incidentally, separates the contact members 38 and 89. The rod 8 is thereupon actuated, in opposition to the force of the spring 7, to force the bar 11 away from the armatures 6a, 6b and 60. If the current is above a previously selected safe value, the flux of the magnetic field will overcome the forces of the springs 80, and the armatures 6a, 6?) and 60 willremain with the steps 32 in engagement with the pole piece 10 (Fig. As the motor accelerates, and the current b gins to die down, the magnetic flux set up by the portion 4a of the coil 4 becomes weakened. After a time, when the flux has de creased to a predetermined value, the spring 30 attached to the armature (M will overcome the force exerted by the flux of this field, so that the relay controlled by the armature 6a will be closed. The time when this operation will occur will depend upon the size of the air gap 34 and the tension of the spring 80. The armatures 6b and 60, however, will remain open.

The closing of the first relay establishes; a circuit which extends from the line conductor 42, through the line switch 51, the armature 6a, the contact members 24 and 26 of the relay controlled by the armature 6a, and the coil 48, to the line conductor 43. The coil 48 becoming energized, the switch 45 becomes closed to shortcircuit a portion of the resistor 44. The motor then further accelerates, and, by decreasing the voltage across the terminals of the coil 4, the mag netic field in the neighborhood of this coil is further weakened, which permits the closing of the second relay, controlled by the armature 65. A circuit is then made from the line conductor 42 through the line switch 51, the armature 6?), the contact members 24 and 26 of the second relay and the coil 49 to the line conductor 43. The coil 49, thus becoming energized, causes the closing of the switch 46 and the consequent shunting of a second portion of the resistor 44-. After the motor has accelerated further, the magnetic field surrounding the portion 4a of the coil 4 is again weakened, and the third relay is closed, creating a circuit extending from the line conductor 42, through the switch 51, the armature 6c, the contacts 24 and 26 of the relay controlled by the armature 60, the coil 50 and the coil 36, to the line conductor 48, thereby causing the energization of the coil 50 and the closing of the switch 47. The whole resistor 44 is then entirely shunted from the armature circuit, and the armature 40 is connected directly across the line.

The shunting of the resistor 44 deenergizes the portion 4a of the coil 4, which would release the armature 5 and cause the relays to be reopened, thus resulting in deei'iergization of the coils 48, 49 and 50 and the consequent reinsertion of the resistor 44 into the armature circuit, except for the portion 36 of the coil 4, which, as may be seen by the circuit just traced, is energized by line voltage.

It will be noted that the motor circuit was established through the cont-act members 38 and 39. lVith these contact members separated, it would be impossible, in the system shown, to start the motor. It is, of course, possible to make the starting of the motor independent 01" those contact members; but, in the system illustrated, the contact members 38 and 39 serve a useful purpose. If, while the motor is running, the stop button is operated, the circuit of the coil 52, extending from the line conductor 42, through the stop switch, the switch 53, and the coil to the line conductor 43, is opened, and the the line switch 51 is, therefore, opened to break the circuit of the motor. The circuit of the portion 86 of the coil 4 and the coil 50, traced above, is also opened at 51; but as the coils are now energized by the counter-electromotive force of the armature 40, the relays and, consequently, the switches 45, 46 and 47, remain closed for a limited time. If the start button were inadvertently or purposely operated during this time, the armature 40 would be thrown directly into the line circuit without any resistance in series with it, were it not that the starting circuit for the motor is open at 88 and 39 as long as there is countcr-electromotive force enough in the armature 40 to energize the portion 36 of the coil 4 with sutficient force to maintain the armature 5 in contact with the pole piece 9. Not until it has come nearly to rest will it be possible to restart the motor.

In Fig. 8, I have illustrated one system in which my switch may be employed. I make no claim to this system here, as it constitutes the subject matter of a separate application, Serial No. 236,937, filed May 27, 1918, by H. D. James, and assigned to the VVestinghouse Electric & Manufacturing Company.

Obviously, my switch may also be employed in other relationships. Furthermore, it is not necessary that the contact members 38 and 89 shall be normally closed in the open position of the armature 5, as illustrated in Fig. 4. It is within the scope of my invention to have the contact member 38 close a circuit, as by making contact with the switch 54, Fig. 7, in the closed position of the armature 5.

It is possible to modify my invention so as to make it applicable to alternating-current circuits. Such a modified switch is illustrated in Figs. 9 to 14, inclusive. The contact-bearing arm 37, of Fig. 4, has, for

clearness, been omitted from the drawings.

To reduce eddy currents, the core 55 is slotted, as shown in Fig. 12, and the brackets 2 and 3 are constructed of coarse laminations 56 into which are inserted shading coils 57 of conventional type to eliminate chattering, as will be understood by those skilled in the art. If desired, the core 55 may be laminated instead of slotted. As there is no danger of ffreezing in alternating-current systems, where the flux is gradually decreased, there is no need here for the bushing 12 or the non-magnetizable stop 32. The armature members 6a, 6b and 6c are, therefore, held in direct contact with the end 58 of the laminated bracket 3, this end 58 serving here as a pole piece. The adjustable gaps 34 of Fig. 4 find their equivalent in adjustable gaps 59 at the rear of the armatures, as in Fig. 1.

It will be understood that the structural details of my switch may be varied and modified from what is shown in the drawings and hereinbefore described, and, consequently, that my invention is not limited except in so far as limitations may be imposed by the prior art or are specifically set forth in the appended claims.

I claim as my invention:

1. In a switch mechanism, the combination with a movable member having an operative position and a plurality of springs for respectively actuating said member in opposite directions with relatively quick snap movements, of an electromagnet for assisting one of said springs, and an armature member for rendering said one spring ineffective when said electromagnet is energize l above a predetermined degree. 1

9.. In a switch mechanism, the combination with means for creating a magnetic field, and a plurality of armatures controlled by said field, of means for successively actuating said armatures in oppositionto said magnetic field, and means for preventing the operation of a plurality of said armatures until one of said armatures has operated.

3. In a switch mechanism, the combination with a movable member having an operative position and a plurality of springs.

for respectively actuating said member in opposite directions with relatively quick 1 movements, of an electromagnet for assisting one of said sprmgs, and an armature member for rendering sald one spring ineffective when saide'lectromagnet is energized above a predetermined degree, the second spring being rendered effective when the. coil is energized below a second and higher predetermined degree.

4. In a switch mechanism, the combination with coil and a pluralityof supporting brackets therefor, one of said brackets being provided with a plurality of projections, of a plurality of armatures, one of said projections serving'as a pole piece for one of said armatures, and another of said projections serving as a pole piece for said other armatures, switchescarried by said other armatures, a spring-pressed rod slidably mounted in said projections to maintain said armatures open, said first armature be ing adapted to depress said rod in opposition to the force of said spring when said coil is energized, and means for successively closing said switches when the current in said coil falls to predetermined values.

5. in a switch mechanism, the combination with a coil, of a slotted core, and a plurality of laminated supporting brackets therefor, shading coils mounted on said brackets, a plurality of armatures adapted to be actuated toward said coil when said coil is energized, and a switch member carried by one of said armatures.

6. In a switch mechanism, the combination with means for creating a magnetic field, of a plurality of armatures adapted to be attracted by the force of said magnetic field and retained in their inoperative positions, and means for successively actuating said armatures to their respective operative positions in opposition to the force of said field. I 7 The combination with a coil and two spring restrained armatures therefor, of a contact member actuated by one armature, the corresponding spring therefor biasing said contact member to its closed position, means for normally maintaining the contact member in its open position, and adapted to be engaged by the other armature when r the coil is energized to permit the other armature to be released when the current traversing the coil falls below a predetermined value. v

at one end thereof, and an armature for each pole piece, of a spring depressed member for normally holding one armature in engagement With its pole piece, a spring for actuating said normally closed armature to its open position, and means whereby the other armature so actuates the spring depressed member as to permit the normally closed armature to operate under predetermined conditions in the coil.

10. The combination With a coil and a main and an auxiliary armature responsiveto the magnetic flux of said coil, of means relaiively movable With respect to said main armature for normally maintaining the main armature in its attracted position, and a spring for actuating said main armature to its operative position, said auxiliary armature being adapted to actuate said relatively movable means when the coil is energized to permit said spring to actuate the main armature to its operative position When the current traversing the coil falls to a predetermined value.

In testimony whereof, I have hereunto subscribed my name this 29th day of May RAY E. DE CAMP.

It is; hereby certified that in Letters Patent No. 1,392,249, granted September 27, 1921, upon the application of Ray E. De Camp, of Wilkinsburg, Pennsylvania,

for an improvement in Current-Limit Relays, errors appear in the printed specification requiring correction as follows: Page 3, line 68, for the Word correspending read success-ice, and line 69, for the Word successive read corresponding; page 4, line 101, for the article the, first occurrence, read these; and that the said Letters Patent should be read With these corrections therein that the same may conform to the record of the case in the Patent Oflice.

Signed and sealed this 29th day of November, A. D., 1921.

KARL FENNING,

Acting Commissioner of Patents.

[SEAL] It is hereby certified that in Letters Patent No. 1,392,249, granted September 27, 1921, upon the application of Ray E. De Camp, of Wilkinsburg, Pennsylvania,

for an improvement in Current-Limit Relays, errors appear in the printed specification requiring correction as follows: Page 3, line 68, for the Word corre- I spending read successive, and line 69,101 the Word successive read corresponding; page 4, line 101, for the article the, first occurrence, read these; and that the said Letters Patent should be read With these corrections therein that the same may conform to the record of the case in the Patent Office.

Signed and sealed this 29th day of November, A. D., 1921.

[SEAL] KARL FENNING,

Acting Commissioner of Patents. 

